Referring to FIG. 1, U.S. Pat. No. 7,213,735 discloses a conventional nail gun 1 that includes a gun body 11, a magazine 12 and a striking unit 13. The gun body 11 has an air chamber 110, an inlet 111 through which compressed air is fed into the air chamber 110, a valve seat 112 that is disposed in the air chamber 110, and a nail path 113 that is formed in a front portion of the gun body 11. The magazine 12 is connected to the gun body 11 for receiving a row of nails (not shown), and pushes the nails into the nail path 113 one at a time. The striking unit 13 includes a cylinder 131 that is disposed movably in the air chamber 110, a nail-striking member 132 that is movable relative to the cylinder 131, a sealing ring 133 that is connected co-movably to the cylinder 131 for being in sealing contact with the valve seat 112, and an operating button 134 that is connected co-movably to the cylinder 131, and that extends out of the gun body 11.
When the operating button 134 is pressed, the cylinder 131 and the sealing ring 133 are driven to form a gap between the sealing ring 133 and the valve seat 112, such that the compressed air flows through the valve seat 112 to drive the nail-striking member 132 to strike one of the nails that is retained in the nail path 113.
However, the nail-striking member 132 performs the nail-striking operation in response to each depression of the operating button 134 even when there is no nail in the nail path 113. The dry firing of the conventional nail gun 1 may be inconvenient for a user.